In recent years, digital documents have been actively shared and distributed via networks such as the Internet or the like. However, since a size limitation is imposed to attach such document to e-mail, a shared document server is set to exchange files based on folder configurations corresponding to companies and organizations that use the server. With this server, documents required for business are shared and distributed using functions of uploading, copying, downloading, and so forth of documents.
However, since data exchange on the Internet is unsure in terms of security, it is desirable to encrypt the contents of documents upon transmitting secret information of a company. For this purpose, when a document is uploaded to an external document management server via the Internet, it is a common practice that the user who wants to transmit the document encrypts the contents of that document by executing an encryption program to the document on a client machine, and then stores the encrypted document in the server.
On the other hand, in order to implement a so-called full-text search which is conducted by designating words that appear in body text of documents so as to meet needs for searching documents stored in the server later, document contents must be scanned in advance to perform language analysis to generate indices. However, the contents of documents which have been encrypted and uploaded by the users cannot be browsed, and it is impossible to generate indices. Hence, Japanese Patent Laid-Open No. 2000-011001 discloses a technique for temporarily decrypting encrypted documents to plaintext to generate search keywords in a server. However, in Japanese Patent Laid-Open No. 2000-011001, since documents are decrypted to plaintext in the server, such technique does not suffice to hide documents from the eyes of the server management agent.
A method of conducting an attribute search by designating various attributes of documents is available. Attributes of documents include a document name, URL, comment, creator, date and time of creation, date and time of update, date and time of access, size, parent folder name, and a user index such as an access right or the like. Some of these attributes are automatically assigned by the system, and some others are manually input by the user.
The user index can be freely set by the user to characterize a document upon registering the document. In the attribute search, a target document can be retrieved by arbitrarily combining these attributes.
However, the attribute search is not adequate to conduct a search using contents written in documents. In consideration of convenience at the time of search, sufficient and appropriate user indices must be manually added upon registration, thus imposing a load on the user.
As described above, since Japanese Patent Laid-Open No. 2000-011001 has a mechanism for decrypting documents into plaintext in the server, it does not suffice to hide documents from the eyes of the server management agent. Also, with the attribute search, the user must individually and manually input appropriate user indices upon registration of documents, thus increasing the load on the user.